It has been known that a reflectance is reduced by applying a coating film having a lower refractive index than that of a base material on the base material. The coating film having a low refractive index is used as an anti-reflective coating in displays such as liquid crystal displays (LCDs), plasma displays (PDPs), and electroluminescence displays (ELs), optical lenses, and screens.
As the anti-reflective coating, an anti-reflective coating made of a multilayer film and having a low residual reflectance has been generally known. When the anti-reflective coating is made of the multilayer film, the multilayer film is produced by a method such as a vacuum evaporation method and a dip coating method. This method is complicated and has economic problems of low productivity and high cost.
In contrast, an anti-reflective coating having a configuration formed of a single layer or two layers has also been known. This configuration requires fewer layer forming processes and is simple, which reduces cost and facilitates mass production. The anti-reflective coating, however, has a problem of a high residual reflectance.
In order to solve the problems as described above, various coating films having low refractive indices have been developed. During this development, it was found that silica sol is a material having a relatively low refractive index and has excellent light transparency in wide wavelength. Besides, it has been known that use of the silica fine particles as a film forming material allows a structure having minute pore spaces among the particles in the obtained anti-reflective coating to be formed, and thus this structure causes decrease in the refractive index of the whole anti-reflective coating, resulting in obtaining an excellent anti-reflective effect. Specifically, a material made by adding the silica fine particles to a photocurable binder (Patent Document 1), a material made by adding the silica fine particles to an alkoxysilane (Patent Document 2), and the like have been described.